Recent years have seen the deployment of a variety of different access standards for use in wireless networks (e.g., GSM, CDMA, WCDMA, IEEE-801.16, etc.). However, the proliferation of wireless access standards has proven to be inconvenient and challenging for the manufacturers of wireless mobile stations (or terminal), such as cell phones, PDA devices, wireless laptops, and the like. End-user expectations of a ubiquitous network cannot be met with mobile stations that support only a subset of the possible standards.
In response, wireless mobile stations are transitioning to software-defined radio (SDR) architectures to provide common hardware platforms for multiple air interface technologies. The continual improvement of semiconductor process technology has enabled an increasingly greater percentage of the signal processing functions in a mobile station (or wireless terminal) to be performed by reconfigurable hardware. The reconfigurable hardware may take one of several forms, including fixed functional blocks with customizable parameters and flexible interconnects. The reconfigurable hardware may be implemented, for example, in a field-programmable gate array (FPGA).
SDR designs must always be cognizant of factors such as current consumption and low component count in order to conserve board space, material cost, and battery life. At the same time, the desire to achieve a roaming capability among different standards requires an SDR receiver to perform faster searches and handoffs. However, the need for faster processing generally requires higher power. The use of field programmable gate arrays (FPGAs) enables SDR devices to perform digital signal processing (DSP) functions at very high speed while consuming lower power than a traditional DSP processor. However, the general trend is that current consumption increases as speed increases.
The state of wireless mobile station development has been that different wireless standards required different hardware. Conventional receiver designs use a zero-intermediate-frequency (ZIF) architecture in which the entire receiver front-end is implemented using analog components. Such a configuration makes it impractical for the receiver to measure the received signal strength for use by the baseband modem. Also, in conventional ZIF architectures, the direct down-converter is a narrowband device that is unsuitable for broadband applications. Other receiver designs digitize at IF frequencies, which results in higher current (i.e., power) requirements. The implementation of configurable hardware for conventional analog-to-digital components at higher frequencies proved too demanding on the current consumption budget.
Therefore, there is a need in the art for a mobile station that implements reconfigurable hardware components in the receiver front-end. In particular, there is a need for a receiver in which reconfigurable components are used prior to the conversion to digital signals at IF level.